This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
1182. The printing process par excellence is undoubtedly the carbon process, employing for the purpose either the stripping film of the Rotary Photographic Company, Ltd., or the ordinary carbon tissue which is now supplied, pigmented in suitable colors, by several manufacturers.
1183. After a long and varied experience, the writer gives the first place to the stripping film method; the reasons being that the balancing of the colors during development is more certain; single transfer only is necessary, the final results are more uniform in quality, and the percentage of failure is smaller than when tissue is employed. Therefore, this is the process selected for detailed description.
1184. The Requisites for this process are: A supply of tri-color film, bichromate of ammonium, methyl alcohol or methylated spirit, strong liquid ammonia, formalin, pure benzine, thin sheet gelatin, white cotton wool, fluffless blotting paper, pins, and a good, wooden-handled camel's-hair mop-brush, about one and a half inches across the hair when dry; or a "Blanchard" brush, made by tying some flannel onto the end of a strip of glass measuring 6 x 1 1/2 inches.
1185. The stripping film is supplied in packets containing twelve pieces, four of each color necessary - red, yellow and blue - and four pieces of transfer paper. The colored pigments are coated onto a base of thin transparent celluloid, through the back of which the print is made.
Ammonium Bichromate .......................
This is best made up in small quantities for immediate use, as the sensitizing qualities of the solution diminish after being made up a few days. For use, a measured quantity is mixed with an equal volume of methylated spirit.
1187. The above sensitizer is suitable for negatives of average density; stronger negatives will require a stronger bath up to 3 drams of bichromate, and weaker negatives a weaker bath, down to 1 dram of bichromate. Negatives requiring a still weaker sensitizer are too thin to give good results, and dense, contrasty negatives are useless for this process.
1188. Before sensitizing, the pigmented surfaces of the films should be carefully rubbed with a soft cloth, to clean off any finger marks.
1189. A film is now laid onto a few thicknesses of blotting paper and fastened down with a pin through each corner. The camel's-hair mop, or Blanchard brush, is well charged with sensitizing solution, which is quickly applied to the film by painting up and down and across. As it is necessary that the film shall be thoroughly saturated, a second brushful of solution may be required. Sensitizing is complete in one minute, and the film should then be put between blotting paper and the superfluous moisture removed from the surface. The film should then be fastened onto a board to dry, a pin being put through each corner.
1190. The sensitizing and drying of films must be done in artificial light, in a well ventilated room. Drying may be assisted by standing the drying boards a few yards away from a fire or radiator, but very quick drying is not advised. The films should be sensitized the evening before they are required for printing, and should be used within twenty-four hours.